The Beauty of Asymmetric Membranes: Reconstitution of the Outer Membrane of Gram-Negative Bacteria.

The architecture of the lipid matrix of the outer membrane of Gram-negative bacteria is extremely asymmetric: Whereas the inner leaflet is composed of a phospholipid mixture, the outer leaflet is built up by glycolipids. For most Gram-negative species, these glycolipids are lipopolysaccharides (LPS), for a few species, however, glycosphingolipids. We demonstrate experimental approaches for the reconstitution of these asymmetric membranes as (i) solid supported membranes prepared by the Langmuir-Blodgett technique, (ii) planar lipid bilayers prepared by the Montal-Mueller technique, and (iii) giant unilamellar vesicles (GUVs) prepared by the phase transfer method.

The mode of action of the lantibiotic lacticin 3147--a complex mechanism involving specific interaction of two peptides and the cell wall precursor lipid II.

Lacticin 3147 is a two-peptide lantibiotic produced by Lactococcus lactis in which both peptides, LtnA1 and LtnA2, interact synergistically to produce antibiotic activities in the nanomolar concentration range; the individual peptides possess marginal (LtnA1) or no activity (LtnA2). We analysed the molecular basis for the synergism and found the cell wall precursor lipid II to play a crucial role as a target molecule. Tryptophan fluorescence measurements identified LtnA1, which is structurally similar to the lantibiotic mersacidin, as the lipid II binding component.

Calcium adsorption and displacement: characterization of lipid monolayers and their interaction with membrane-active peptides/proteins.

Background: The first target of antimicrobial peptides (AMPs) is the bacterial membrane. In the case of Gram-negative bacteria this is the outer membrane (OM), the lipid composition of which is extremely asymmetric: Whereas the inner leaflet is composed of a phospholipid mixture, the outer leaflet is made up solely from lipopolysaccharides (LPSs). LPS, therefore, represents the first target of AMPs.

Lipid-specific membrane activity of human beta-defensin-3.

Defensins represent a major component of innate host defense against bacteria, fungi, and enveloped viruses. One potent defensin found, e.g.

Lipid-mediated resistance of Gram-negative bacteria against various pore-forming antimicrobial peptides.

Lipopolysaccharides (LPSs) play a dual role as target and as effector molecules. The knowledge of the LPS-induced activation of human immune cells is increasing; however, surprisingly, much less effort seems to be directed towards the understanding of the mechanisms leading to the killing of the bacterial organisms, which eventually results in the release of LPS from the bacterial surface into the blood circulation. We demonstrate mechanisms of interaction of peptides of the innate immune system (e.

Inner field compensation as a tool for the characterization of asymmetric membranes and Peptide-membrane interactions.

Symmetric and asymmetric planar lipid bilayers prepared according to the Montal-Mueller method are a powerful tool to characterize peptide-membrane interactions. Several electrical properties of lipid bilayers such as membrane current, membrane capacitance, and the inner membrane potential differences and their changes can be deduced. The time-resolved determination of peptide-induced changes in membrane capacitance and inner membrane potential difference are of high importance for the characterization of peptide-membrane interactions.

Pore formation and function of phosphoporin PhoE of Escherichia coli are determined by the core sugar moiety of lipopolysaccharide.

The lipid matrix of the outer membrane of Gram-negative bacteria is an asymmetric bilayer composed of a phospholipid inner leaflet and a lipopolysaccharide outer leaflet. Incorporated into this lipid matrix are, among other macromolecules, the porins, which have a sieve-like function for the transport or exclusion of hydrophilic substances. It is known that a reduced amount of porins is found in the outer membrane of rough mutants as compared with wild-type bacteria.